Urban rail transit in India plays an important role in intracity transportation in the major cities which are highly populated. It consists of rapid transit, suburban rail, monorail and tram systems. According to a report published in 2021, a total of 2.63 billion people travelled annually in metro systems across India's fifteen major cities, placing the country as one of the busiest urban rapid transit hubs in the world in terms of ridership. The combined length of 810 kilometres (500 miles) of metro systems in India makes it the fourth longest in operation in the world.